Erythema induratum: a rare case with unusual presentation

Tuberculosis, still one of the most common infectious diseases globally, manifests primarily as pulmonary tuberculosis. Extra-pulmonary tuberculosis can occur in other sites including skin. Cutaneous tuberculosis, comprising merely 1-2% of all forms of tuberculosis, has been classified into various morphological variants. One of the morphological variants of cutaneous tuberculosis is erythema induratum, a tuberculid, which is caused by hematogenous spread of tuberculosis, the pathogenesis of which is due to hypersensitive reaction against the mycobacterial antigens. The skin biopsy findings of erythema induratum are characterized by panniculitis with formation of non-caseating epithelioid granulomas with no mycobacteria detected in the lesions, though mycobacterial antigens or DNA could be detected by polymerase chain reaction (PCR). In this context, being presented here is a case of erythema induratum which is rare and unusual in its presentation inasmuch as caseating epithelioid granulomas were seen in the lesional skin biopsy along with detection of acid-fast bacilli. In our study a 57-year-old male presented to the Dermatology OPD with multiple erythematous lesions bilaterally over the groin and thigh regions. Clinically the lesions were considered to be equivocally suggestive of migratory erythema or erythema marginatum. The skin biopsy taken from the lesions revealed multiple epithelioid granulomas in the dermis with central areas of caseation necrosis. Sections stained with Ziehl-Neelsen stain showed the presence of occasional acid-fast bacilli. Erythema induratum, a rare tuberculid form of cutaneous tuberculosis, which is pathogenetically considered to be occurring as a result of hypersensitivity reaction against mycobacterial antigens with characteristic absence of tubercle bacilli. In the case presented here erythema induratum presents in a rare unusual manner as a caseating granulomatous lesion with presence of demonstrable acid-fast bacilli.